1. Field of the Invention
The present invention is directed generally to an AM radio transmitter. More particularly, the present invention is directed to a VHF band AM radio transmitter of the type utilized for general aviation purposes. More specifically, the present invention is directed to a unique AM radio transmitter having an electrical configuration that produces an extremely low order of harmonics.
2. Description of the Related Art
AM radio transmitters are widely used in the aviation industry as communication devices. These devices have a microphone input, processing circuitry, and an antenna output. An operator, such as a pilot or navigator, speaks into a microphone and an audio signal, indicative of the input voice is generated, modulated onto an RF carrier, amplified and output through the antenna. Traditionally, transmitters for the aviation market are constructed with Class C bipolar transmitters. Conventional AM radio transmitters utilized in the aviation industry have a high order of harmonic emissions. These emissions radiate from the antenna port of the transmitters, as well as in a general fashion off of the transmitter device itself.
Specifically, many conventional AM radio transmitters for the aviation industry utilize what is known as a high level modulation for the collector of the final device in the transmitter stream. In these devices, a power supply voltage is actually modulated to modulate the AM radio signal.
The high order of harmonic emission associated with conventional prior art devices is undesirable. In order to reduce the harmonic emissions, complex and expensive filter units must be employed. Additionally, these filtering units are not altogether effective, resulting in the prior art devices having poor electromagnetic characteristics, both from their antenna ports, and radiating off the devices themselves.
Accordingly, the need exists for a simple solution to the problem of high order harmonic emissions from an AM radio transmitter. Particularly, the need exists for an efficient AM transmitting device which has a low order of harmonic emissions. The present invention overcomes the drawbacks of the prior art, and fills these and other needs.